The hibernation file you really only need for hibernation - not for sleep mode. It is the size of your RAM. Go into an elevated command prompt and paste this commannd in:
powercfg.exe -h off
Then hit Enter. That will get rid of it. If you use Acronis for imaging on a regular basis, you can also stop the system restore points (shadowstorge). That will save you another few Gigabytes.
I run Win7 in a 42GB partition (on an SSD). I have 1700 progam folders (11.450 files) and my system uses 15.2GB. I think you should be OK with a 40GB partition. If it is a spinning disk, defrag it. That may gain some too.